Ornithine aminotransferase (OAT) deficiency is a condition caused by not having enough of the OAT enzyme, leading to a significant increase in the amino acid ornithine in the body. Symptoms and how the disease progresses can vary from person to person.
The first signs usually show up in late childhood and include problems with night vision and reduced side vision because the retina, a part of the eye, is degenerating. Complete blindness typically doesn’t happen until a person is in their 40s or 50s because the disease progresses slowly. Many people with this condition also become nearsighted and develop cataracts in their late teens or early 20s. Besides issues with vision, most patients don’t have other symptoms. However, a few may experience mild muscle weakness, sensory problems, or mild to moderate intellectual disability. In rare cases, newborns with OAT deficiency may have high ammonia levels, leading to symptoms like vomiting, poor feeding, diarrhea, seizures, and coma. Some studies suggest that slowing down the progression of the disease might be possible by reducing the amount of ornithine in the body. People with OAT deficiency are often put on diets that are low in arginine or low in protein. In a small number of cases, patients have shown improvement by taking high doses of vitamin B6, which helps decrease ornithine levels.
OAT is caused by pathogenic (disease-causing) variants in the OAT gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Sephardic Jewish descent have a 1 in 177 chance to be a carrier.
Other names for this condition are gyrate atrophy, hyperornithinemia with gyrate atrophy of choroid and retina, ornithine keto acid aminotransferase deficiency, ornithine-delta-aminotransferase deficiency, and ornithinemia with gyrate atrophy.